1. Field of the Invention
The present invention relates to methods and apparatus for contacting integrated circuits for tests before they have been packaged. More particularly, the present invention relates to test probes and methods for aligning the test probes with a semiconductor die prior to testing.
2. Prior Art
As integrated circuits have become smaller and more complex, early detection of faulty parts has become more important in managing and containing costs. Packaging costs have escalated significantly, especially with respect to the more complicated devices. In some circumstances, packaging can cost more than the silicon die itself. Accordingly, testing on the wafer or die level to eliminate faulty devices has become increasingly important. Testing of an integrated circuit at the die level requires the use of a probe card to make contact with the bonding pads on the die.
Currently, there are three probe card styles that are in general use: ceramic blade, metal blade, and epoxy ring. In each of these probe cards an array of long delicate needles or wires is attached to the probe base and the wires are cut and bent in such a way that the ends correspond to the bonding pads on the semiconductor die being tested. As semiconductor devices have become more complicated and have included more circuits, the number of bonding pads and thus, the number of wires on a probe has had to increase.
The material and length of the wires being used depends upon various factors including contact force, contact resistance, power requirements and density requirements. Even with optimization, these wire probes offer relatively poor electrical performance for high speed signals.
The fragility of the needles on a probe can also cause a number of problems. For example, they are easily bent so that they are out of alignment or do not otherwise make contact with the pad. Much of this is simply the result of the numerous touchdowns which occur as large batches of devices are tested by a single probe.
Another problem associated with these probes is proper alignment. The ends of the needles must be visually aligned with the pads to which they correspond before touchdown and contact occur. This slows down the testing process and provides another source of possible error to the testing procedure.
A new technology which is being developed to test semiconductor dies involves the use of membrane probe cards. According to this technology, a flexible, dielectric membrane supports a set of microstrip transmission lines that connect the test electronics to the pads on the die being tested. The transmission lines are formed by a conductor trace pattern on one side of the dielectric membrane. A contact bump is formed on the other side of the membrane at the end of each transmission line and is connected to the transmission line through a hole in the membrane. An example of this technology is disclosed by B. Leslie and F. Matta, "Membrane Probe Card Technology (The Future For High Performance Wafer Test)," Proceedings IEEE International Test Conference, pp. 601-607 (1988). Some of the advantages of this technology are discussed by C. Barsotti, S. Tremaine and M. Bonham, "Very High Density Probing," Proceedings IEEE International Test Conference, pp. 608-614 (1988).
While these membrane probe cards promise many advantages over the prior art, they still have certain drawbacks. First, the flexible dielectric membrane has a different coefficient of thermal expansion than the semiconductor die thus, potentially causing alignment problems when the die is tested at temperature extremes. Additionally, these probe cards require that the dielectric material be transparent so that the probes can be visually aligned with the bonding pads on the die being tested.
Accordingly, it would be an advancement in the art to provide a semiconductor probe and alignment system in which the probe is durable, permitting repeated touchdowns without the need for readjustment, and is compatible with high pin count dies. It would be a further advancement in the art if such a probe were made from materials having similar properties as the die being tested.
It would also be an advancement in the art to provide a system whereby a probe card could automatically be aligned such that the contactors made contact with the bonding pads on the die being tested.